Separation of anthracene-cake constituents



Patented May 4, 1948 2,440,688: 'SEEARKTIQNDF ANTHR CENE-GAKE- CONSTITUENTS 'Th'omasr'llaroldflnsinger, Jrz, Pittsburgh; Pa, as-

zsig'nolt, mesneassignments, to. KoppersComa many; Inc, acorporation of. Delaware.

No Drawing, Implication January 7, 1943, "Serial N0. 471,626?

The present invention. relates to methods for obtaining highly purified anthracenefrom crude anthracene cake. V V

' An object of the present invention is} improvenients inmethodsof ermoloyi'ng-ft he Weil -known reaction between ant hracene and inal'eic anhydride, for separatingrefinedanthrao'ene from crude anthracenawhereby tlie' nsefulne'ssi of the employed 'maleic reagent is importantlyimproved.

A furtherobject ot'the presentinvention is the provision ofimprovements/whereby a soluti'on of maleic acid, either in water or other solverit; i can be directly employed for the recovery of refined anthracene from its} cr'ud'es. H

A further object ofinvcntionis iinprovement in methods for the 'therni'aiidissociation ot the anthracene-mal'eidanhydride condensation product whereby 'improveerecovry beo'oineapossime of its malei'c component-"ion reuse iorthe stated,

tion product being thereai ter senaratedjirom associated impurities and; thermally dissociated to recover purified "anthracene, preferably by methods disclosed a; copendin-g application of Charles F. Winan's SeriarNo. 1395,694 filed May 281. 1941, now Patent 2;347,228-, and wherein said) separation is effected, for exampie, by alkaline extraction of said condensation product from impurities followed by liberation! of anthracenemaleic anhydride-iby.acidulationof the extract. in a further-step, isfltherea'iter dissociated by means including a heat into Sits-starting materials; that into pure. 'anthracene "and; imaleicianhydride, or into maleicra'cid' in'those'instances where steam is employedas a carrier-vapor rMaleio-acid must somehow FIIEI'QQIIWEiZtQd; to 'maleic- (anhyd-ride before it is again condensable with anthracene. V

. I is etnqwe i -"een er a e w to the za-nhydride by means including heat and either The so-separ'ated condensation: product;

with or without additionof chemical agents.

Under the infiuenceyoi heat, there; is a; definite tendency-howeverfor maleic acid to convert, to f-umaric acid in undesirable =01, uneconomical proportiona andfumaric acid is unemployable as such for formation of said condensation product of anthracene; Thus,, 0he reemployment of a given quantity of maleicyacid,v or its anhydride, for separating anthracene froniits crudes will soon exhaust it-a fact that, because of its cost, has heretofore made'i-tsuse' for the purpose-economic'ally questionable V V i However, it has nowbBenr'f'Qund' that ii, in the recovery of refined anthracene from its erodes, for example, the crude anthracene cakeproduced by distillation of coaltar, themaleiaaoidis, dehydrated: to maleicanhydride in-sitirwhiie incontact with anthracene, the formation of-v saidcondensation product tends to goon while maleic anhydride is in a sorttnascent form, and that the tendencyof mal'eic acid to convert into a iumaricacid is-importantly-reduced, and soflmuch so, that the total loss occasioned is lesszthan 2 percentin asin-gle cycle of a pnocess-for using this material in the formation of said condensation product from impure anthracene oake.,-

According to the present invention. therefore anthracene, in crudes containing phenanthrene, carbazole, and the like, is; treated for its conversion to. the anthraoene-maleic anhydride "product while in direct contact with. a source. of

7 acid either as such. or in aqueous or other solventmedia. In the practice. oitrthe invention, the'anthracenecrude,- While in. solution in a solvent therefor, and preferably a, toichiometric quantity or maieic. acid are heated in h gpr keno'eof each. other under conditions to efiect the dehydration of the maleio. acid to maleicanhY- dride whichv thereuponouickly diSSOIV Bdln the solvent and combines. with the also dissolved ancthracene to form anthracene-maleic anhydride.

For example, the anthracene cake is dissolved in such solvent medium therefor as xylenejdecalin,

oyclohexanone, ortho-dichlorobenzene, 'nitro bencovery of refined anthracene.

zene, phenylether, or in purified coke-oven solvent naphtha having a boiling range of about 160 C. to 180 C., and to which may be added if preferred, but not necessarily, certain proportions of a lower-boiling solvent such, for example, as benzeneor toluene. To this solution is added an amount of maleic acid that is preferably stoichiometrically equivalent to the anthracene component of the dissolved cake and the mixture is boiled under reflux, the vapors being condensed in a refluxing device adapted to segregate water and any of the employed solvent medium simultaneously distilled therewith, the latter being continuously returned to the distillation equipment for reuse. The maleic acid can be introduced into the said solution of anth'racene cake either as a solid, or it can be ex-.

tracted from an aqueous solution thereof previously formed in the process system, as hereinafter set forth, by an appropriate solvent such as cyclohexanone which can then be employed as above stated for dissolving the anthracene cake, or such aqueous solution of maleic acid can be introduced into the reaction vessel containing the dissolved anthracene :cake and the waterphase can then be removed by appropriate distillation and reflux before the actual conversion of the maleic acid into its anhydride, the temperature being increased as the removal of the water phase nears completion and the latter reaction begins to take place. Cyclohexanone is of advantage for the present purpose because it exhibits solvent properties for both maleic acid and its anhydride as well as also anthracene cake thus the condensation reaction can be carried out with all the reactants in single-phase solution. Xylene, toluene, benzene, and the like, are good solvents for maleic anhydride but have little. solubility forvmaleic acid; thus, when they are employed as the solvent medium, the latter must be first converted by the said boiling step, to the therein, soluble maleic anhydride which is then quickly dissolved and rapidly converts the dissolved anthracene into soluble anthracenemaleic anhydride.

Following the condensation reaction, the formed anthracene-maleic anhydride product 'is separated or removed from the solvent in which the impurities are dissolved; for example, by an appropriate solvent extraction and preferably by means of an aqueous solution of an alkali which forms a corresponding salt of the acid form of the anhydride complex. This extraction step is then followed by acidulation and liberation of the insoluble free acid: i. e., anthracene-maleic acid. However, if a-cidulation is carried out above about 80 C. there is directly liberated from the aqueous extract the water-insoluble anthra- 4 of, as hereinabove described, or its maleic acid content can be extracted from said aqueous solution by means of an appropriate solvent such as cyclohexanone and this solvent solution itself can be of the extracted maleic acid employed in the reaction vessel. The solvent employed for dissolution of the crude anthracene and for carrying out the described reaction can be of relatively narrow boiling range or of wide boiling range, the latter type of solvent being preferable in those instances where an aqueous solution of maleic acid is introduced directly into the reaction vessel. The process may be practiced stepwise a or continuously with recycling of recene-maleic anhydride itself. Thereafter, the

said productis dissociated by heat for the re- This dissociation is preferably carried out, in the presence of a sweep vapor, at less than atmospheric pressure and at high temperature; for example, vapors of the heated anhydride are passed in the presence of steam and at a pressure of about 30 millimeters mercury absolute through reactor appa ratus maintained at about 400 C. The vapors effluent to the reactor are shock chilled and the liberatedrefined 'anthracene is separated from the associated aqueous solution of maleic acid by filtration, or .thelike. This aqueous solution of maleic acid is then available for its recycling directly to the reaction vessel for recovery of further quantities of anthracene from crudes there ent novel process.

Example 1 4013 parts anthracene cake containing 42.4% of anthracene, the other constituents being predominantly phenanthrene and carbazole, were dissolved in 8000 parts of refined coke-oven solvent naphthaiboiling range 160 C.-180 C.) and 2900 parts benzene, to which was added 1137 parts maleic acid in aqueous solution, 930 parts thereof being recycled from a, previous operation of the present improved process for refining anthracene. This admixture was heated, with condensationof vapors, by means automatically providing separation of condensed water and continuous selective return of the condensed solvent vapors to the reaction vessel. Subsequent to the removal of the aqueous phase, the amount of benzene returnedto the reaction vessel was diminished with diminishing removal of water. At the end of the reaction period, which is indicated by absence of both water and benzene in the condensate, the residue in the reaction vessel was cooled to about 100 C. and then successively treated by heating-first with a 3 per cent, and thereafter with a per cent solution of sodium hydroxide, accompanied by continuous return of all condensed vapors, the said 3 per cent solution being obtained from a subsequent process step. The anthracene-maleic anhydride product was thereby substantially completely extracted from solvent as sodium anthracene-maleate. The solvent portion, after separation from said aqueous extract, was distilled and the distillate recycled to the initial step. The residuum can be successfully treated for the separation of carbazole and phenanthrene. The hot aqueous extract was then acidified between about 80 C. and 100 0., with vigorous'stirring, by means of sulphuric acid to neutralize excess alkali and liberate free anthracene-maleic anhydride. The latter said product, under about 27 millimeters mercury absolute pressure, was then melted and vaporized with and in the presence of superheated steam at about 230 C. to 260 0., and a mixture of the vaporsand steam was then flowed through a heated'zone maintained at about 400 C., the contact time being'about 0.3 second, and the prod-' of'filterei washd and" driedeake, -yvere: anthra- "cen having a greater thari 98 peneentpurtty and representd'a yield of 93;8 per cent of the origin-a1 anthraeene present ut the riitial'ferude.

-am'ined.

Example 2 "I -he eflioiency of I 'tformation ref 1' anthracene- :maleic aanhydride ziaccording= to. athe present :in-

vention is shown zby t the itfoliowing aldata. i100 parts of an raqueous lso'lution zcontaining abont benzene, 100: partsidecalm andi25martseanthra- 'cene (97.2:perrdenttpune). -'I he;'sai'd admixture;

"was :heated, '--wi th condensation of vapors, "by means automatically providin'gaseparationzofz con- ".idensed Water @and'rsele'ctive return Ibf the eonidensed solvent vapors ito ithe freact'ien {VESSEL 'rsubsequent to the rem-oval. t-oflthe:aqueousmha'se,

- theamount-of benzene return to thezreaction-vessel was' diminishedv with diminishing.fremovalz of water. Atrthe endfofi th eaetion periodi which :issindicated byrebsence. both' water and' benfzene'iinithe condensate}the-residue iri' thereaotion as vessel was cooied to about Floo -neared?experts sodiumlhydroxidei inki-fioozpartsrwateriwere added.

The new mixture was"refluxd 'fofi two houra then "cooled tdmo C.-8Iidthe aqueous dayernrawn off,

after which fa .parts 135 mmeent sodimxnydroidde 'solution rim-200- parts --water were added -Lto the 1 decalinilayer and the miitture refluxed ror an hour,""followed by -separation of he F two laye'rs.

The two aqueous extracts were comhined d-ilutd with water and heated 170 85 ci bfire add ftibn f formed by this novel proce'dure, had-a melting z range of :259;0'-'C.-260I5 C.tarrd representd an overall yieldzaof 19816 per eentfr'orn the quantity of maleic acid employed.

Example 3 The 'eflioiency :of sdissociation :tr: the vproduct prepared'sinfixamplem carried" out according: to the "present: improvement, is shown: :by 1 the rol- -lowing' results. 500 pantssanthracenemaleicitanhydride "were-melted and' vaporized*iwithkandsin the presence. oi snperheated ssteam :at'iabOutt-EOO" 7 C.," a'nd theresultingvvaporswere thereafter'flowed v throughra zonei maintainedz atiaboutMOO C., the 'contact time ibeing about 4 seconds and the absolute pressurexaboutl29i5 millimeters ofinr- 3G0mvnfionfpmvides"that the anthracne -ma1eic am hydride is "dissociated' at'reduced pressures and .inther-prsenceof.steam at about-400 C.'..u'sing reontactlt'imes (if-0.3 and OA seconds. The'process "alsoigives high,.recoverable yields of anthracene 'and maleic "acid at contact times of from"0.01 ssecond to "5 seconds. Dissociation of -anthraoenemaleic anhydridecan be efiected with 1 steam and t t 'lessthan atmosphericpressureswithin a term perature rangedefined by the meltiiig point of antl iracene-mal'ei'c anhydride and fbelOW about ti' 5002-'C.,' =at which' temperature loss "of the maleic component begins :to occur by "Pyrolysis.

cury; The 'products of densedfitheimaleic aeid isdlution filtered o 'resu1ting"'filter cake was boiled' withlito per eent sodium' hydroxide so lution torr'emeve nndissoei- "ated condensation product therefrom :and the then remaining filter cake mashed dried. Analysis;of the separated 'prdduetsishowed a recovery of: 309':parts anthraeene haying a pdrity of"99.4 per cent; ramparts-manic aetd tnlwater solution; 6 parts I anthracene' imaieic airi hydride I v product; and '29 parts= earbonaceous residue and unaccounted-for losses. This repie'sents a dis- 'sociation efiiciency *of -95T8 per cent in atsirrgle cycleoroperationsantl wmaleic acid-*recovery ot '6 Examples! The efliciency of fonnatiomof anthraeenemaleic anhydride by employment of' a-fsingle solvent for the'fanthracene" isshown by thefol- "lowing'results. 236 parts ofan aqueous-solution containing about42i7 partsmaleid aeidwere adtr'n'ixd with"1300 partsx'ylene t'boiling'i'r'ange 135 C. 140"C.) and 130 parts rfinedarithraceneicake cohtaining"90l3per cent of anthraceneQ'Thesaid f admixture" was boiled; the vapors th'rfrdnifbeiiig "condensed and the resultant condensate, comprising "water and *xylene, were 'iseparated,

with returner "thexy'lene" as refiuxto theizreaction finesse]. At the end ofthelreaction'period,'which is indicated by absence"of Watenin 'the'con- 'd'n'satef the residue in the "'reaction""ve' ssel"was extracts werejcombined, diluted With"Wi;ter" aT1jd heated t0"'8 5 C. before additiondf concentrated sulphuric acid to precipitate "anthracene-inaleic condensation product extracted by the alkali f'romthe solvent. "After acidificationfthe premaleic anhydrlde represented 97.7" parts, an ove all yield-of 96.2 per centfrom"tlie quantitypf ima'leictacid employed.

"The" process offinventionis obviously of utility for synthesizing anthracenemaleidacid, or its anhydride, Or any preferred salts thereof'from starting materials that are substantially pure.

:Fseparation of so-formed anthracenemaleic anhy dride from the employed solvent medium can be also effected, for example, by crystallization or dist'illation,'-aswell' as by liquid extraction.

The invention can be practiced by employing for the'crude anthracene a solvent having'a' narrrow'or 'a'relative'ly wide-boiling range; for'example, xylene, or refined heavy solvent naphtha,

or in'fact'an'y solvent material that boils withina temperature range of about 80 'C. and the meltting'fpoint of Tan anthracene-maleic anhydride product. Of utility also is a'so'lvent agent that is' a mixture of' a"low-boi1ing and a'high-lboiling ;'material;"fori example, a mixture of" benzene and those'of the hydroxidesand carbonatesof the alkali meta'ls andalkaline earth metals.

idcidied int particrrlar form andi'mar'merihutsrnay be I-claim:

variously embodied within the scope of the claims hereinafter made.

1. In a process for separating refined anthracene from crude anthracene containing phenanthrene, carbazole, or the like, by means of its linkage with the maleic radical, the improvement comprising the steps of heating said crude anthracene while in solution in inert solvent means therefor in the presence of maleic acid to. a temperature that is suificient 'simulta neously to vaporize both water and solvent means from the resultant mixture and also to effect concurrently a linkage between anthracene of its said crude and maleic anhydride that is formed in situ in said mixture by the aforesaid vaporization of said water therefrom, and thereby concurrently dehydrating the maleic acid and forming anthracene-maleic anhydride therewith in the solution; separating from the resultant mixture a compound containing the anthracene-maleic linkage formed during the aforesaid heating; flowing the aforesaid compound containing the so-formed anthracene-maleic linkage, in the presence of steam and at a subatmospheric pressure, through reactor means at sufiiciently elevated temperature to effect scission of said anthracene-maleic linkage; condensing vapors effiuent to said reactor means; and separating from said condensed efiluent both refined anthracene and aqueous solution of maleic acid produced by the aforesaid scission of said anthracene-maleic linkage.

2. In a process as claimed in claim 1, the step of-re-employing in the first said step maleic acid that is recovered in the last said step as such for the separation of refined anthracene from a further quantity of its crude.

3. In a process as claimed in claim 1, the steps of employing, in the first described step of said method, aqueous maleic-acid solution that has been previously separated according to the described last step thereof by a prior practice of the process, and also vaporizing the'aqueous phase of said maleic-acid solution in situ in the first step by. heating and vaporizing of the inert solvent means containing the crude anthracene in solution in the first step.

4. A process as claimed in claim 1, and which includes the steps of extracting the maleic acid content from the aqueous solution of the last step of said claimed process with cyclohexanone and introducing the same to the first step of said process.

5. In a process for separating refined anthracene from crude anthracene containing phenanthrene, parbazole, or the like, by means of its linkage with the maleic radical, the improvement comprising the steps of: heating said crude anthracene while in solution in inert solvent means thereior in the presence of maleic acid to a temperature that is sufficient simultaneously to vaporize both Water and solvent means from the resultant mixture and also to effect concurrently a linkage between anthracene of its said crude and maleic anhydride that is formed in situ in said mixture by the aforesaid vaporization of said water therefrom, and thereby concurrently dehydrating maleic acid and forming anthracenemaleic' anhydride therewith in the solution; separating from the resultant mixture a compound containing the anthracene-maleic linkage formed during the aforesaid heating; flowing the aforesaid compound containing the so-formed anthracene-maleic linkage, in the presence of steam and at an' absolute pressure ofabout 30 mm, through reactor :means maintained between about 400-500 0.; maintaining said mixture of steam and said compound at between about 0.01 to v5 seconds in contact with said heated reactor means, to effect scission of said anthracenemaleic linkage; condensing vapors eiliuent to said reactor means; and separating fromsaid condensed effluent both refined anthracene and aqueous solutionof maleic acid produced by-the aforesaid scission of said anthracene maleic linkage.

6. In a process for separating refined anthracene from crude anthracene containing phenanthrene, carbazole, or the like, by means of its linkage with the maleic radical, the improvement comprising the steps of heatingsaid crude anthracene while in solution in inert solvent means therefor in the presence of maleic acid to a temperature that is sufiicient simultaneously to vaporize both water and solvent means from the resultant mixture and also to effect concurrently a linkage between anthracene of its said crude and maleic anhydride that is formed in situ in said mixture by the aforesaid vaporization of said water therefrom, and thereby concurrently dehydrating maleic acid and forming anthracenemaleic anhydride therewith in the solution; separating from the resultant mixture a compound containing the anthracene-maleic linkage formed during the aforesaid heating; flowing the aforesaid compound containing the so-formed anthracene maleic-linkage through reactor means at temperature sufiiciently high to elfect scission .of said anthracene-maleic linkage, and ata contact time of between about 0.01 and 5 seconds; condensing vapors efiluent to said reactor means; and separating fromsaid condensed effluent both refined anthracene and a compound of said scission containing uncombined maleic radical.

7. In aprocess for separating refined anthracene from crude anthracene containing phenanthrene, carbazole, or the like by means of its linkage with the maleic radical comprising: dissolving crude anthracene in a solvent; adding aqueous maleic acid thereto; distilling thesolution to drive off free water; raising the distillation temperature after the water is removed, to dehydrate the maleic acid, to distill off water separated from the maleic acid along with solvent, and to'link maleic anhydride formed with anthracene to form a maleic anhydride-anthracene compound; condensing and separating the water and solvent removed by distillation; and

returning solvent to the distillation zone.

8. Theprocess defined in claim 7, and in which the anthracene and maleic acid are added in stoichiometric proportions to form the anthracene-maleic anhydride compound, and in which maleic acid is gradually dehydrated to supply maleic anhydride to form said compound, and in which benzene is employed as the solvent and is continuously returned to the distillation zone from the separation step until the maleic acid is dehydrated to form maleic anhydride to unite with all-of the anthracene. I

9. The process defined in claim 7, and in which the anthracene and maleic acid are added in 'stoichiometric proportions to form the anthrais continuously returned to the distillation zone from the separating step until the maleic acid is 9 dehydrated for forming said a compound, and which includes the step of thereafter distilling off any remaining water and benzene solvent from the distilling zone to separate them from the anthracene-maleic anhydride compound.

10. The process defined in claim 7, and in which the solvent is made up of two components, one of which boils above the boiling temperature of water and the other of which is lower boiling and forms an azeotrope with water to assist in removing the water from the distillation zone.

11. The process defined in claim 7, and in which the solvent is made up of two components, one of which boils above the boiling temperature of water and is added in sufficient quantity to dissolve the crude anthracene, and the other of which is lower boiling and is added in suflicient The following references are of record in the file of this patent:

UNITED STATES PATENTS I Date Number Name 1,966,853 Dvornikoff July 17, 1934 2,340,490 Porter Feb. 1, 1944 OTHER REFERENCES Paliakova, Organic Chem. Ind. (U. S. S. R.) '7, 305-8 (1940). (Copy in 260-675). 

